The present invention relates to a capacitor, such as, for example, an electrolytic capacitor, having a housing part, having at least one capacitor reel which includes two capacitor electrodes insulated from each other by a dielectric and is positioned in the housing part, and having a housing bottom which has at least one feed-through for contacting the capacitor electrodes, and at which outer terminals are arranged for the capacitor electrodes.
Such capacitors may be used in practice, for instance, as back-up capacitors in power supply units or as intermediate circuit capacitors, where they may function as energy storage mechanisms. In order to achieve this object, even in connection with rapidly changing signals, they may need to have as low an inductance as possible.
FIG. 1 shows a design of such a capacitor 100, as an exploded illustration. Capacitor 100 includes a capacitor reel 102, which forms the actual capacitance. Capacitor reel 102 is made of two capacitor electrodes 103 and 105 in the form of metal foils, of aluminum, for example, which are insulated from each other by a dielectric. A paper sheet 104 soaked in electrolyte is used here as the dielectric. Thus, capacitor 100 may also be denoted as an electrolyte capacitor. A high capacitance may be implemented in the smallest space by the wound arrangement of the layer sequence 103, 104, 105. For clarity, capacitor reel 102 is shown here partially unwound. Capacitor reel 102 is positioned in a beaker-shaped housing part 101, that may be made of metal. In addition, capacitor 100 includes a housing bottom 109, made of an electrically insulating material, on which are arranged two metallic terminals 110 and 111 for the positive pole and the negative pole of capacitor 100. In the case of large-volume capacitors, as indicated, these outer terminals 110 and 111 are outfitted each with a thread for the screw connection of outer supply leads. Capacitor 100, capacitor electrodes 103 and 105 may be connected to outer terminals 110 and 111 via supply leads 106 and 107 inside the capacitor.
In FIGS. 2a and 2b, two variants 100 and 200 of the above capacitor design of FIG. 1, are shown here in cross section, the cross sectional planes here each running through outer terminals 110 and 111. It should be noted at this point that the same objects are provided with the same reference marks in all the Figures.
In the capacitor variant 110 of FIG. 2, supply leads 106 and 107 inside the capacitor are arranged in the outer region of capacitor reel 102 and are guided vertically upwards to outer terminals 110 and 111 positioned on housing bottom 109. Unwanted inductance of capacitor 100 may result from the design and the arrangement of outer terminals 110 and 111 and current supply leads 106 and 107 internal to the capacitor. Capacitor variant 200 shown in FIG. 2b is discussed in: J. Roumen, xe2x80x9cNew Aluminum Electrolytic Capacitors with Low Inductance Allow Advanced Frequency Converter Designxe2x80x9d, PCIM 2000 Conference Proceedings, Session PC, PC6.6. Here, the unwanted inductance in capacitor reel 102 may be reduced by optimization of internal current leads 206 and 207. For this purpose, supply leads 206 and 207 may be positioned further inside capacitor reel 102, compared to supply leads 106 and 107 illustrated in FIG. 2a, and may be guided outwards at an angle to outer terminals 110 and 111.
FIGS. 3a and 3b represent a capacitor 200 before its connection to busbar construction 300. As a cross sectional representation after connection to busbar construction 300, outer terminals 110 and 111 of capacitor 200 are contacted via busbar construction 300. Busbar construction 300 includes two metallic conductors 302 and 303 arranged parallel next to each other on an electrically insulating carrier 301, and these are the actual busbars. Capacitor 200 is electrically connected to the two busbars 302 and 303 by two screws 310 and via two washers 311, and is at the same time mechanically fixed to busbar construction 300. A busbar construction may not be ideal, due to the additional conductance that may result. However, the mechanical construction may fit well with the terminal layout of capacitor 200.
The exemplary embodiment of the present invention concerns a capacitor of the kind referred to above that has a reduced inductance compared to other capacitors, and which may permit in a simple manner the use of low-inductive current supply leads such as busbars.
According to the exemplary embodiment of the present invention, this may be achieved by having one of the two outer terminals surround the other outer terminal at least partially, and by having the two outer terminals electrically insulated from each other. By an arrangement of the two outer terminals of the capacitor, both the external current supply line as well as the internal current supply line to the capacitor reel may be implemented with very low inductance. Furthermore, the arrangement of the two outer terminals may provide a constructively simple current supply lead to the capacitor reel and simple connection of low-inductive busbars.
There may be additional embodiments and arrangements of the outer terminals of the capacitor according to the present invention, where one of the two terminals encircles the other terminal at least partially. One capacitor variant, in which the two terminals are arranged essentially coaxially and are designed essentially cylinder-shaped, may result in a low additional inductance. But capacitor variants whose terminals are not executed coaxially, and capacitor variants in which the outer lying terminal does not encircle the inner lying terminal completely in a circular cylindrical shape, may also lie within the framework of the present invention.
With a view to the desired reduction in additional inductance, at least one of the outer terminals may be arranged essentially coaxially with the capacitor reel. If the feed-through in the bottom of the housing is also essentially arranged coaxially with the capacitor reel and the outer terminals, the current supply lead to the capacitor reel may also be designed very simply. In this connection, at least one of the outer terminals may reach through the feed-through in the housing bottom into the inside of the housing part, and may directly contact the appropriate capacitor electrode. In one exemplary embodiment of the capacitor according to the present invention, at least the outer terminal arranged to lie inside reaches into the inside of the housing part and may thus be used as winding spindle for the capacitor reel.
The outer terminals of the exemplary capacitor according to the present invention may be furnished with a fastening arrangement for the purpose of fixing outer current supply leads. Screw threads, for instance, may be suitable as a fastening arrangement for screw fastening the current supply leads. In the case of current supply leads in the form of busbars, by using screw fastening, one may establish a pressure connection between the busbars and the corresponding outer terminals, which may ensure good electrical contact.